IS31LT3360 AIC DEMO BOARD GUIDE
Integrated Silicon Solution, Inc. – www.issi.com 2
Rev. A, 08/31/2015
ORDER INFORMATION
Part No. Temperature Range Package
IS31LT3360-SDLS3-EBAIC
IS31LT3360-SDLS4-EBAIC
-40°C to +105°C (Industrial)
-40°C to +125°C (Industrial)
SOT89-5, Lead-free
For pricing, delivery, and ordering information, please contacts ISSI’s analog marketing team at
analog@issi.com or (408) 969-6600.
DETAILED DESCRIPTION
LED Current Control
The nominal average output current in the LED(s) is
determined by the value of the external current sense
resistor (R
S
) connected between V
IN
and I
SENSE
and in
is given by:
I
OUT nom
= 0.1/R
S
[for R
S
>0.082Ω]
The table below gives values of nominal average
output current for several preferred values of current
setting resistor (R
S
) in the typical application circuit
shown on Page 1:
R
S
(Ω)
Nominal Average Output
Current (mA)
0.082 1200
0.1 1000
0.15 667
0.3 333
V
SENSE
is divided into two range to improve current
accuracy, please refer to bin information on Page 2.
The above values assume that the ADJ pin is floating
and at a nominal voltage of V
REF
=1.2V.
Note that R
S
=0.082Ω is the minimum allowed value of
sense resistor under these conditions to maintain
switch current below the specified maximum value.
It is possible to use different values of R
S
if the ADJ pin
is driven from an external voltage.
Inductor Selection
Recommended inductor values are in the range 47μH
to 220μH.
Higher values of inductance are recommended at
higher supply voltages and low output current in order
to minimize errors due to switching delays, which
result in increased ripple and lower efficiency. Higher
values of inductance also result in a smaller change in
output current over the supply voltage range. The
inductor should be mounted as close to LX pin as
possible with low resistance connections to LX and V
IN
pins.
PCB Layout Consideration
Decoupling Capacitors and Coil
It is particularly important to mount the coil and the
input decoupling capacitor close to the chip to
minimize parasitic resistance and inductance, which
will degrade efficiency. The input decoupling capacitor
(0.1μF fixed) must be placed as close to the V
IN
and
GND pins as possible. It is also important to take
account of any trace resistance in series with current
sense resistor R
S
.
LX Pin
The LX pin of the chip is a fast switching node, so PCB
traces should be kept as short as possible. To
minimize ground 'bounce', the ground pin of the chip
should be soldered directly to the ground plane.
ADJ Pin
The ADJ pin is a high impedance input, so when left
floating, PCB traces to this pin should be as short as
possible to reduce noise pickup. ADJ pin can also be
connected to a voltage between 1.2V~5V. In this case,
the internal circuit will clamp the output current at the
value which is set by V
ADJ
=1.2V.
High Voltage Traces
Avoid running any high voltage traces close to the ADJ
pin, to reduce the risk of leakage due to board
contamination. Any such leakage may raise the ADJ
pin voltage and cause excessive output current. A
ground ring placed around the ADJ pin will minimize
changes in output current under these conditions.
